The incorporation of chirally pure phosphorothioates into oligonucleotides can be effected by utilizing various DNA polymerases and the appropriate phosphorothioate monomers. It has been reported that the presence of a single Rp- as opposed to Sp-linkage at one of the chiral P's in phophorothioates leads to an increased Tm (temperature at which hybridization is 50% complete). Thus, the Rp isomers are able to form a more stable duplex with their complements and this has implications in antisense therapeutics and probe technology. We propose to synthesize chirally pure all-Rp and all Sp phosphorothioate oligonucleotides for testing of this hypothesis. In a 15-mer phosphorothioate there are potentially more than 15,000 different chiral compounds. This heterologous chirality may have pronounced effects upon the ability of these oligonucleotides to act efficiently in antisense therapy. This study will evaluate the importance of chirality at the phosphorothioate linkages for antisense and hybridization technology.